Is it possible to make a shotgun reflux condenser too big?

[FuelMaker]

I'm building a 4" VM, input heat is 22566 W / 77000 BTUs (110k BTU steam injection boiler derated for losses). The condenser is a standard tube-in-shell using 3/8" tubing and will have baffles internally every 4".

I've gone round-and-round with the parent site calculator but what it's telling me is I need something like 780 inches of 3/8 tube and I'm not sure I believe it. Several comments from other posters about that particular calculator makes me tend to not trust it.

An added wrinkle is that I want to run this using a closed loop using natural thermosyphon flow for the cooling at an educated guess about 1-2 L/min which will be pretty slow water movement compared to a pump. I don't actually know if it can be done using just convection flow but I'm going to try. I might have to reduce input power a lot to work. The thermosyphon flow is why I'm going with the shell-in-tube design - its the least flow restrictive of all the designs.

If I go with my gut instinct to just "go big" and make a 4" wide by 20 inch long condenser w/ as many 3/8 tubes as I can pack in while still giving me a 1/8 gap between them and it turns out to be horribly oversized will it screw things up? Or just waste a lot of copper.

My only goal is azeo, and I'm not too concerned with smearing either. When I want to make potables I'll add a LM module for fores/heads removal and run things a whole lot slower.

I'd actually be making two condensers of the same size/build; a reflux-and-product mode (at reduced power at just under flooding conditions), and a potstill mode - which means the product condenser needs to be able to handle the max heat input when doing a rip-snorting max power stripping run, because it's steam injection it shouldn't scorch.

I could probably get away with making the reflux condenser smaller because the load will be shared with the PC in reflux mode - but once I get the jigs done for the PC it'll actually be easier to make two of the same size.

I need some advise from somebody with experience to guide me since I keep changing my mind every other minute...

Thanks!

[bearriver]

It is my understanding that you are not likely to have negative impacts from overbuilding an RC, but you can under build one and/or overcool one by pushing too much coolant.

Have you seen a csst condenser? Its dirt cheap and can be made in about 3 minutes without any skill. My personal favorite for LM and VM type stills. I am shocked that they arent more common...

[DAD300]

The only possible bad affect of a condenser being too big or too effective is if you can not "throttle down" the water entering it. As in if the RC or PC is so cold and so close to the take off, that it cools the column and or packing and slow/stop takeoff.

[FuelMaker]

Thanks for the replies! I'm very reassured. I'd like to do a CSST but the passive coolant flow precludes it - especially since I'm about to have 89 FEET of leftover 3/4" stainless CSST from the steam generator build (it was cheaper to buy the roll vs by-the-foot). Dunno what I'm going to do with it, maybe make another steam generator and sell it to recoup the cost or just sell it by-the-foot here.

[cranky]

Thanks for the replies! I'm very reassured. I'd like to do a CSST but the passive coolant flow precludes it - especially since I'm about to have 89 FEET of leftover 3/4" stainless CSST from the steam generator build (it was cheaper to buy the roll vs by-the-foot). Dunno what I'm going to do with it, maybe make another steam generator and sell it to recoup the cost or just sell it by-the-foot here.

Makes me wish I needed some. Isn't 3/8 a little small for a reflux condenser? I don't see why 89 feet of CSST couldn't be used for passive coolant flow.

[drmiller100]

22,000 watts?????? GOOD GOD!!!!!!!!!!!!!!

how big is your boiler? 100 gallon?

[rubber duck]

22,000 watts?????? GOOD GOD!!!!!!!!!!!!!!

how big is your boiler? 100 gallon?

Sounds like 150-200 gallons . If someone is running that many amps and is asking questions about condensers I don't want to be involved.

[FuelMaker]

Nope the boiler is 25 gallons, it's a maple syrup barrel. The natural gas burner is leftover from a wood gasification experiment a few years ago and I want to reuse it. I almost certainly wont be able to run it at full power without a massive puke (might be able to mitigate that w/ a integrated slobber box though), but I'm trying to design it to be able to knock down max output. Just in case.

It'd be pretty cool to do a stripping run at max power, I'll just have to see how it performs.

At any rate I finally came across this post from feb 2013:

I have a 48" liebig on my 2" potstill (30" tall)
It will knock down everything my 5500W element will throw at it, however at full power the distillate comes out too warm to proof read. I usually run it around 4500W on a stripping run

I'm making a guess his inner pipe is 1/2".

So now I have some real-world numbers. 5500 watts at 48 inches gives me 114.6 watts per inch giving me a total length of 197 inches for me at max power using half inch pipe. I'll do the numbers of watts per square inch of surface area later.

If I stick with the 20" shotgun length it rounds out to 10 pipes using 1/2" pipe, I'll have to convert via the surface area equivalents when using 3/8" refer tubing. I'm going by the hardware store tomorrow and I'll pick up tubing caps and see how many I can pack into a 4" circle.

Because shotguns are more efficient than liebigs (though I don't know how much more 10% 20% 40%??) I can probably reduce my length a bit.

[googe]

Is your PC 4" shell?. Im a bit confused what's what. As for the rc, like pfshine said, 4~6" will knock down most. I've found alot of smaller inner tubes can be fickle with control issues. Larger seems more user friendly. I use 4x1" inner tubes in 4" shell and performs well, can knock down most and is quick to respond. PC, I use a shotgun with 4x1/2" in 2" shell. But of you want a stripper as well, you can't beat a 3 walled liebig, I did one 2.5" outer shell, 2" middle shell and 1" inner tube, could knock down everything I could through at it using a 600kpa burner running on 220kpa, flames lapping the side side of the keg and it could still keep up, 19.8lph.

[drmiller100]

I know for a FACT 4800 watts is about max that a 3 inch column with marbles can run.

So, 22,000 btus will need a column with about 6 times more cross section area for reflux.

3 inch column is 3x3x3.14 = 28 square inches.

6 times bigger is 6x28 = 170 square inches.

170 square inches, round, is squrt(170/3.14) = 7.5 inch column as a place to start.

I realize you are running a pot still, but your numbers are crazy big.

[FuelMaker]

Is your PC 4" shell?. ... I've found alot of smaller inner tubes can be fickle with control issues. Larger seems more user friendly...

Its a 4" shell using copper DWV pipe. Thanks for the advice on the smaller tubes, I grabbed caps for 1/2 refer tubing too and it looks like I'll be able to have 12 1/2 tubes in there, maybe 1 more if I crowd it more than I want. Refrigeration tubing is slightly smaller than regular copper pipe. It means I'll be able to shrink it to 17" long.

That 3 walled liebig sounds pretty cool to, I'll have to think about that.

[john2674]

Just for reference purposes I have a 3 inch shotgun 24 inches long with 7 half inch tubes and 7 baffles inside it. that works out to 168 inches of pipe inside it. I have 11000 watts of power available,
It will handle everything my still can throw at it ..... right up until it pukes... I just cant run that much power even in pot still mode
when I first built mine the masters also warned me about the dangers of scorching when pushing too much heat into the wash, I'm not sure if your looking for fuel ethanol or drinking, so that may or may not be a concern for you.
as for me 5500- 7000watts is about max that my pot can take on a stripping run. that's still pretty fast though.
Edit; I just noticed the steam injection bit... Hmm it would sure be interesting to see what that baby could do! I have no idea how to keep the rig from puking though that's a little above my pay grade i'm afraid.

[shadylane]

I'm building a 4" VM, input heat is 22566 W / 77000 BTUs (110k BTU steam injection boiler derated for losses

I think that's too much power for a 4" column

An added wrinkle is that I want to run this using a closed loop using natural thermosyphon flow

Why use use thermo syphon to power the cooling water flow? It makes problems, when your looking to limit problems.

My only goal is azeo, and I'm not too concerned with smearing

Is azeo alcohol needed? Or would a lower ABV work just as well.

[Prairiepiss]

So you are wanting to do a thermal siphon coolant?

If you don't have a good flow going through it. The water in the shotgun can easily start boiling very quickly.

But I kinda like the idea. Don't think it will work as you have described it.

[shadylane]

It could work, with a big enough RC, a radiator and a fan blowing on it.
But if there's power for the fan then there's power for a pump.
I'm running a 4" CM. The shot-gun dephleg is 8" long with eight 1/2" tubes.
A garden hose is almost enough for full reflux at 9kw
And is too big for accurate control when making a run.

[FuelMaker]

I guess I should clarify; I want to have the ability to run it pumpless, but I'm very aware I'll have to severely restrict power when I do. Normal operation will be using a pump.

I know if I try to reflux at max power all I'll do is flood it, the only time I'll ever to do a max power run is when I'm making distilled water for the steam injection rig - it might cost a little more than buying it, but at least I won't have to lug dozens of gallons of water around.

The limiting factor is going to be column flooding in reflux mode, and puking in potstill mode. It'll be a matter of learning my rig to find out at what power levels that happens at.

In potstill mode I guess I could try flocculating the wash, filtering out all the solids, and using a defoamer, but I'll probably just reduce the power - it's easier.

I'm planning on having sight glasses in the lid of the boiler, and at the bottom of the column just so I can visually see when it starts to puke.

John, thanks for the info on your shotgun! Your numbers will help me dial in how long I have to make the condensers.

[shadylane]

Just a thought.
If you want a RC without a pump or running water, search aircooled condensers.

[drmiller100]

7.5 inch diameter column. Probably 10 feet of packimg.

[Scribbler]

Bigger is better!!

[rad14701]

So, 22,000 btus will need a column with about 6 times more cross section area for reflux.

22,000 BTU's is just shy of 6,500 Watts... Proper conversions help make sense of things... We have members throwing 10,000 Watts into 15.5 gallon beer kegs during warmup...

EDIT: Ahh... I see numbers got mixed up through the progress of this topic... 77,000 BTU's converts to 22,500 Watts...